Used to adjust and control a substance at an atomic or molecular level, nanotechnology is suitable to create novel substances and materials, and applied to various fields, such as electronic, material, communication, mechanical, medical, agricultural, energy, and environmental fields.
Currently, development of various types of nanotechnologies is in progress, and the nanotechnology is usually classified into the following three categories. The first category relates to a technology to synthesize ultrafine novel substances and matter using a nano-material. The second category relates to a technology to produce a device which assures predetermined functions by combining or arranging nano-sized materials. The third category relates to a technology to apply a nanotechnology, which is called a nano-bio, to bioengineering.
Particularly, in nano-bio fields, nanoparticles are used to specifically kill cancer cells, boost an immune reaction, fuse cells, deliver genes or drugs, conduct diagnosis and the like. In order to apply the nanoparticles to the above applications, the nanoparticles must have portions, to which active components are capable of adhering, and must be stably delivered and dispersed in vivo, that is, in a water-soluble environment. Many technologies have lately been developed to satisfy such conditions.
U.S. Pat. No. 6,274,121 discloses paramagnetic nanoparticles including metals, such as iron oxides, to which inorganic materials, having binding sites that are capable of being coupled with tissue-specific binding substances and diagnostically or pharmaceutically active materials, adhere.
U.S. Pat. No. 6,638,494 pertains to paramagnetic nanoparticles containing metals, such as iron oxides, and discloses a method of preventing nanoparticles from cohering and precipitating in the gravity or magnetic fields, in which specific carboxylic acid adheres to surfaces of the nanoparticles. Examples of the above carboxylic acid include aliphatic dicarboxylic acid, such as maleic acid, tartaric acid, and glucaric acid, or aliphatic polycarboxylic acid, such as citric acid, cyclohexane, and tricarboxylic acid.
U.S. Pat. No. 6,649,138 discloses a method of improving the water-soluble property of nanoparticles, in which a multiply amphiphilic dispersant layer is formed on surfaces of the hydrophobic nanoparticles having semiconductor or metal materials. The multiply amphiphilic dispersant is exemplified by (1) a hydrophobic backbone having hydrophilic branched chains, (2) a hydrophilic backbone having hydrophobic branched chains, or (3) a hydrophobic or hydrophilic backbone simultaneously having hydrophilic and hydrophobic branched chains.
U.S. Patent Application No. 2004/0033345 discloses a method of capsulizing nanoparticles, in which hydrophobic ligand layers are formed around metals or semiconductors, using micelles to dissolve the nanoparticles in an aqueous solution. At this time, the micelles consist of hydrophilic shells and hydrophobic cores.
U.S. Patent Application No. 2004/0058457 suggests functional nanoparticles which are surrounded by monolayers, and in which bifunctional peptides adhere to the monolayers and various biopolymers including DNA and RNA are bound to the peptides.
However, the water-soluble nanoparticles produced according to the above method, have the following disadvantages. In U.S. Pat. Nos. 6,274,121, and 6,638,494, and U.S. Patent Application No. 2004/0058457, the nanoparticles are synthesized in aqueous solution. In such a case, it is difficult to control the sizes of the nanoparticles, and the synthesized nanoparticles have a nonuniform size distribution. Furthermore, since they are synthesized at low temperatures, crystallinities of the nanoparticles are low and non-stoichiometric compounds are apt to be generated. Additionally, surfaces of the nanoparticles are coated with a monomolecular surface stabilizer, but bonding strengths between the stabilizer and the nanoparticles are not high, and thus, the nanoparticles are less stable in aqueous solution. The water-soluble nanoparticles of U.S. Pat. No. 6,649,138 and U.S. Patent Application No. 2004/0033345 are surrounded by amphiphilic polymers, thus having significantly increased diameters in comparison with inorganic nanoparticles. Further, successful application examples of these nanoparticles are limited to semiconductor nanoparticles.